Semiconductor device and manufacturing method thereof

ABSTRACT

Provided is a semiconductor device includes a gate stack, a first doped region, a second doped region, a first lightly doped region and a second lightly doped region. The gate stack is disposed on a substrate. The first doped region is located in the substrate at a first side of the gate stack. The second doped region is located in the substrate at a second side of the gate stack. The first lightly doped region is located in the substrate between the gate stack and the first doped region. The second lightly doped region is located in the substrate between the gate stack and the second doped region. A property of the first lightly doped region is different from a property of the second lightly doped region.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of and claims the priority benefit ofU.S. application Ser. No. 15/482,829, filed on Apr. 10, 2017, nowallowed. The entirety of the above-mentioned patent application ishereby incorporated by reference herein and made a part of thisspecification.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Over the course of this growth, functional density of thedevices has generally increased with the device feature size.

In order to meet the requirements for smaller sizes and higher packingdensities, the IC includes a semiconductor device with differentproperties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A through FIG. 1B are schematic cross-sectional views illustratinga manufacturing process of a semiconductor device according to a firstembodiment of the disclosure.

FIG. 2 is a flowchart illustrating a manufacturing method of thesemiconductor device according to the first embodiment of thedisclosure.

FIG. 3A through FIG. 3E are schematic cross-sectional views illustratinga manufacturing process of a semiconductor device according to a secondembodiment of the disclosure.

FIG. 4 is a flowchart illustrating a manufacturing method of thesemiconductor device according to the second embodiment of thedisclosure.

FIG. 5A through FIG. 5F are schematic cross-sectional views illustratinga manufacturing process of a semiconductor device according to a thirdembodiment of the disclosure.

FIG. 6 is a flowchart illustrating a manufacturing method of thesemiconductor device according to the third embodiment of thedisclosure.

FIG. 7A and FIG. 7C are schematic cross-sectional views illustratingsemiconductor devices according to a fourth embodiment of thedisclosure.

FIG. 7B is a schematic top view illustrating the semiconductor device ofFIG. 7A.

FIG. 7D is a schematic top view illustrating the semiconductor device ofFIG. 7C.

FIG. 8 is a flowchart illustrating a manufacturing method of thesemiconductor device according to the fourth embodiment of thedisclosure.

FIG. 9A to FIG. 9C are schematic cross-sectional views illustrating asemiconductor device according to a fifth embodiment of the disclosure.

FIG. 10 is a flowchart illustrating a manufacturing method of thesemiconductor device according to the fifth embodiment of thedisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a second feature over or on a first feature in the description thatfollows may include embodiments in which the second and first featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the second and first features,such that the second and first features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath”, “below”, “lower”,“on”, “above”, “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

FIG. 1A through FIG. 1B are schematic cross-sectional views illustratinga manufacturing process of a semiconductor device according to a firstembodiment of the disclosure. FIG. 2 is a flowchart illustrating amanufacturing method of the semiconductor device according to the firstembodiment of the disclosure.

Referring to FIG. 1A and FIG. 2, in step S10, a substrate 100 isprovided. The substrate 100 includes a bulk substrate, asilicon-on-insulator (SOI) substrate or a germanium-on-insulator (GOI)substrate, for example. In one embodiment, the substrate 100 includes acrystalline silicon substrate (e.g., wafer). The substrate 100 mayinclude various doped regions depending on design requirements (e.g.,p-type substrate or n-type substrate). In some embodiments, a dopedregion 101, formed in the substrate 100, may be a well, a buried dopedregion, or a combination thereof. In some embodiments, the doped region101 and the substrate 100 have the same conductivity type. In somealternative embodiments, the doped region 101 and the substrate 100 havedifferent conductivity types. In some embodiments, the doped region 101may be doped with p-type or n-type dopants. For example, the dopedregion 101 may be doped with p-type dopants, such as boron, BF₂ ⁺,and/or a combination thereof, n-type dopants, such as phosphorus,arsenic, and/or a combination thereof. In some alternative embodiments,the substrate 100 may be made of some other suitable elementalsemiconductors, such as diamond or germanium, a suitable compoundsemiconductor, such as gallium arsenide, silicon carbide, indiumarsenide, or indium phosphide, or a suitable alloy semiconductor, suchas silicon germanium carbide, gallium arsenic phosphide, or galliumindium phosphide.

Referring to FIG. 1A and FIG. 2, in step S10, isolation structures 102are formed in the substrate 100. In some embodiments, the isolationstructures 102 may be shallow trench isolation (STI) structures. Theisolation structures 102 include silicon oxide, silicon nitride, siliconoxynitride, a spin-on dielectric material, a low-k dielectric material,or a combination thereof and formed by performing a high-density-plasmachemical vapor deposition (HDP-CVD) process, a sub-atmospheric CVD(SACVD) process, or a spin-on process, for example.

The substrate 100 may include a first region R1, a second region R2, anda third R3. In some embodiments, the first region R1 and the thirdregion R3 may be periphery regions, for example, I/O regions, and thesecond region R2 may be a core region.

Referring to FIG. 1A and FIG. 2, in step S11, an implantation process 10is performed on the substrate 100. The implantation process 10 may be ablanket ion implantation process, so that an implantation species isimplanted into the doped region 101, the sidewalls and bottom of theisolation structures 102, a junction interface 101 a between the dopedregion 101 and the substrate 100 in the first region R1, the secondregion R2 and the third region R3, or a combination thereof. As aresult, defects and trap residues in the substrate 100 may be reduced.The implantation species may include fluorine (F). The implantationprocess 10 may be performed at a range of energy values and dosages. Insome embodiments, the energy values may range from 30 keV to 80 keV, andthe dosage may range from 1×10¹³/cm² to 1×10¹⁵/cm².

Referring to FIG. 1B and FIG. 2, in step S12, a first device D1, asecond device D2, and a third device D3 are formed on the substrate 100in the first region R1, the second region R2, and the third region R3respectively. The first device D1, the second device D2, and the thirddevice D3 may be the same or different. In some embodiments, the firstdevice D1, the second device D2, and the third device D3 are a firstmetal-oxide semiconductor (MOS) device, a second MOS device, and a thirdMOS device respectively. The first MOS device includes a first gatestack 104 and first doped regions 110. Similarly, the second MOS deviceincludes a second gate stack 204 and second doped regions 210; and thethird MOS device includes a third gate stack 304 and third doped regions310.

In some embodiments, the first gate stack 104 includes a first gatedielectric layer 106 and a first gate electrode 108. Similarly, thesecond gate stack 204 includes a second gate dielectric layer 206 and asecond gate electrode 208. The third gate stack 304 includes a thirdgate dielectric layer 306 and a third gate electrode 308. In someembodiments, the first, second, and third gate dielectric layers 106,206, and 306 include silicon oxide, silicon nitride, silicon oxynitride,high-k dielectric materials, or a combination thereof. The high-kdielectric materials are generally dielectric materials with adielectric constant higher than 4. The high-k dielectric materialsinclude metal oxide. In some embodiments, examples of the metal oxideused as the high-k dielectric materials include oxides of Li, Be, Mg,Ca, Sr, Sc, Y, Zr, Hf, Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb, Lu, or a combination thereof. The gate dielectric layers 106,206, and 306 are formed by performing a thermal oxidation process, a CVDprocess, an ALD process, or a combination thereof respectively. In someembodiments, the first, second, and third gate dielectric layers 106,206, and 306 have different thicknesses. For example, the first gatedielectric layer 106 is thicker than the third gate dielectric layer306, and the third gate dielectric layer 306 is thicker than the secondgate dielectric layer 206.

The first, second, and third gate electrodes 108, 208, and 308 areformed on the first, second, and third gate dielectric layers 106, 206,and 306 respectively. In some embodiments, the first, second, and thirdgate electrodes 108, 208, and 308 are polysilicon gate stacks orreplacement metal gate stacks. A material of the first, second, andthird gate electrodes 108, 208, and 308 include a doped polysilicon, anundoped polysilicon, or a metal-containing conductive material. Themetal-containing conductive material includes a work function layer, aseed layer, an adhesion layer, a barrier layer, or a combinationthereof. The metal-containing conductive material includes Al, Cu, W,Ti, Ta, Ag, Ru, Mn, Zr, TiAl, TiN, TaN, WN, TiAlN, TaN, TaC, TaCN,TaSiN, NiSi, CoSi, or a combination thereof, for example. In someembodiments, the gate electrodes 108, 208, and 308 includemetal-containing conductive materials suitable for a PMOS device, suchas TiN, WN, TaN, or Ru. In some alternative embodiments, the first,second, and third gate electrodes 108, 208, and 308 includemetal-containing conductive materials suitable for an NMOS device, suchas Ti, Ag, Al, TiAl, TiAlN, TaC, TaCN, TaSiN, Mn, or Zr. The first,second, and third gate electrodes 108, 208, and 308 may be formed byperforming a suitable process such as an ALD process, a CVD process, aPVD process, a plating process, or a combination thereof.

The first, second, and third doped regions 110, 210, and 310 are formedin the substrate 100 beside the first, second, and third gate stacks104, 204 and 304 respectively. The first, second, and third dopedregions 110, 210, and 310 may be source and drain regions respectively.In some embodiments, the first, second, and third doped regions 110,210, and 310 have the same conductivity type dopants or differentconductivity type dopants. In some embodiments, the first, second, andthird devices D1, D2, and D3 are PMOS devices, and the first, second,and third doped regions 110, 210, and 310 have p-type dopants, such asboron, BF₂ ⁺, and/or a combination thereof. In some alternativeembodiments, the first, second, and third devices D1, D2, and D3 areNMOS devices, and the first, second, and third doped regions 110, 210,and 310 have n-type dopants, such as phosphorus, arsenic, and/or acombination thereof. In some alternative embodiments, the first, second,and third doped regions 110, 210, and 310 have different conductivitytype dopants.

In some embodiments, the first, second, and third devices D1, D2, and D3further include first, second, and third lightly doped source and drain(LDD) regions 112, 212, and 312 respectively. The first LDD regions 112and the first doped regions 110 have the same conductivity type.Similarly, the second LDD regions 212 and the second doped regions 210have the same conductivity type. The third LDD regions 312 and the thirddoped regions 310 have the same conductivity type.

Via the blanket ion implantation of fluorine into the substrate, thedevice noise can be significantly reduced.

FIG. 3A through FIG. 3E are schematic cross-sectional views illustratinga manufacturing process of a semiconductor device according to a secondembodiment of the disclosure. FIG. 4 is a flowchart illustrating amanufacturing method of the semiconductor device according to the secondembodiment of the disclosure.

Referring to FIG. 3A, FIG. 3C, and FIG. 4, in step S30, a substrate 100is provided. The substrate 100 may include a doped region 101 andisolation structures (not shown) formed therein. The substrate 100 mayinclude a first region R1, a second region R2, and a third R3. In someembodiments, a first dielectric layer 106 c, a second dielectric layer206 a, and a third dielectric layer 306 c are to be formed on thesubstrate 100 in the first region R1, the second region R2, and thethird region R3 respectively. The first dielectric layer 106 c isthicker than the third dielectric layer 306 c, and the third dielectriclayer 306 c is thicker than the second dielectric layer 206 a.

In some alternative embodiments, the first region R1 and the thirdregion R3 may be periphery regions, for example, I/O regions, and thesecond region R2 may be a core region. For, example, a first device D1,a second device D2, and a third device D3 (shown in FIG. 3E) are to beformed in the first region R1, the second region R2, and the thirdregion R3 respectively. The first device D1, the second device D2, andthe third device D3 may be a first MOS device, a second MOS device, anda third MOS device respectively. Further, a threshold voltage of thefirst MOS device in the first region R1 is greater than a thresholdvoltage of the third MOS device in the third region R3.

Referring to FIG. 3A and FIG. 4, in step S31, a mask layer 130 having anopening 132 is formed on the substrate 100. The mask layer 130 coversthe second region R2 and the third region R3, and the opening 132 of themask layer 130 exposes the first region R1. In some embodiments, themask layer 130 is a patterned photoresist layer.

Referring to FIG. 3A and FIG. 4, in step S32, an implantation process 30is performed on a surface of the substrate 100 by using the mask layer130 as a mask. The implantation process 30 may be an ion implantationprocess, so that an implantation species is implanted into the dopedregion 101 in the first region R1. As a result, a growth promotingregion 134 is formed in the doped region 101 in the first region R1. Theimplantation species may include growth promoting species, such asfluorine (F). The implantation process 30 may be performed at a range ofenergy values and dosages. In some embodiments, the energy values mayrange from 5 keV to 15 keV, and the dosage may range from 1×10¹⁴/cm² to1×10¹⁶/cm².

Referring to FIG. 3B and FIG. 4, in step S33, the mask layer 130 isremoved to expose surfaces of the doped region 101 in the first regionR1, the second region R2, and the third region R3. The mask layer 130may be removed by an ashing process, a wet clean process, or acombination thereof.

Referring to FIG. 3B, FIG. 3C, and FIG. 4, in step S34, a gatedielectric layer forming process is performed on so as to form the firstdielectric layer 106 c, the second dielectric layer 206 a, and the thirddielectric layer 306 c on the doped region 101 in the first region R1,the second region R2, and the third region R3 respectively. In someembodiments, the gate dielectric layer forming process may include thefollowing processes.

Referring to FIG. 3B and FIG. 4, in step S35, a first oxidation processis performed, so as to form a first dielectric layer 106 a, a seconddielectric layer 206 a, and a third dielectric layer 306 a on the dopedregion 101 in the first region R1, the second region R2, and the thirdregion R3. Because the growth promoting region 134 is formed in thefirst region R1 and not formed in the second region R2 and the thirdregion R3, the first dielectric layer 106 a is thicker than the seconddielectric layer 206 a and the third dielectric layer 306 a, and thesecond dielectric layer 206 a and the third dielectric layer 306 a havesimilar thicknesses. In some embodiments, the first oxidation process isa thermal oxidation process, a high temperature oxidation process, or acombination thereof. The first oxidation process may be performed at atemperature range from 800° C. to 1200° C.

Referring to FIG. 3C and FIG. 4, in step S36, a block layer 136 havingan opening 138 is formed on the substrate 100. The block layer 136covers the second region R2, and the opening 138 of the block layer 136exposes the first region R1 and the third region R3. The block layer 136may be a single layer or multiple layers. In some embodiments, the blocklayer 136 is formed of a dielectric material layer. The dielectricmaterial layer may be silicon nitride formed by performing a suitableprocess such as an ALD process, a CVD process, a PVD process, a platingprocess, or a combination thereof, for example. Thereafter, thedielectric material layer is patterned by performing a photolithographicprocess and an etching process.

Referring to FIG. 3C and FIG. 4, in step S37, a second oxidation processis performed by using the block layer 136 as a mask, so as to form afirst dielectric layer 106 b and a third dielectric layer 306 b on thedoped region 101 in the first region R1 and the third region R3respectively. The second region R2 is covered by the block layer 136,therefore the thickness of the second dielectric layer 206 a is notincreased significantly.

As a result, the first dielectric layer 106 c, the second dielectriclayer 206 a, and the third dielectric layer 306 c are formed on thedoped region 101 in the first region R1, the second region R2, and thethird region R3 respectively. The first dielectric layer 106 c includesthe first dielectric layer (first part) 106 a and the first dielectriclayer (second part) 106 b, and the third dielectric layer 306 c includesthe third dielectric layer (first part) 306 a and the third dielectriclayer (second part) 306 b.

The first dielectric layer 106 c is thicker than the third dielectriclayer 306 c, and the third dielectric layer 306 c is thicker than thesecond dielectric layer 206 a. In some embodiments, the thickness of thefirst dielectric layer 106 c is about 55 angstroms to about 60angstroms, the thickness of the third dielectric layer 306 c is about 41angstroms to about 51 angstroms, and the thickness of the seconddielectric layer 206 a is about 15 angstroms to about 25 angstroms.

Referring to FIG. 3C, FIG. 3E, and FIG. 4, in step S38 and S39, theblock layer 136 is removed by an etch process such as an isotropic etchprocess. A first device D1, a second device D2, and a third device D3are formed on the substrate 100 in the first region R1, the secondregion R2, and the third region R3 respectively. The first device D1,the second device D2, and the third device D3 include a first gatedielectric layer 106, a second gate dielectric layer 206, and a thirdgate dielectric layer 306. The first, second, and third gate dielectriclayers 106, 206, and 306 are formed from the first dielectric layer 106c, the second dielectric layer 206 a, and the third dielectric layer 306c.

In some embodiments, the first device D1, the second device D2, and thethird device D3 are a first metal-oxide semiconductor (MOS) device, asecond MOS device, and a third MOS device respectively. The first MOSdevice includes a first gate stack 104 and first doped regions 110.Similarly, the second MOS device includes a second gate stack 204 andsecond doped regions 210; and the third MOS device includes a third gatestacks 304 and third doped regions 310. In some embodiments, the first,second, and third devices D1, D2, and D3 further include first, second,and third lightly doped source and drain (LDD) regions 112, 212, and 312respectively.

In some embodiments, the first gate stack 104 includes the first gatedielectric layer 106 and a first gate electrode 108. Similarly, thesecond gate stack 204 includes the second gate dielectric layer 206 anda second gate electrode 208. The third gate stack 304 includes the thirdgate dielectric layer 306 and a third gate electrode 308.

In the embodiments, in which the first device D1, the second device D2,and the third device D3 are the first MOS device, the second MOS device,and the third MOS device respectively, the first device D1, the seconddevice D2, and the third device D3 may be formed by the followingprocesses.

Referring to FIG. 3D and FIG. 3E, a gate material layer 408 is formed onthe first dielectric layer 106 c, the second dielectric layer 206 a, andthe third dielectric layer 306 c. A material of the gate material layer408 includes a doped polysilicon, an undoped polysilicon, or ametal-containing conductive material. The metal-containing conductivematerial includes a work function layer, a seed layer, an adhesionlayer, a barrier layer, or a combination thereof. The metal-containingconductive material includes Al, Cu, W, Ti, Ta, Ag, Ru, Mn, Zr, TiAl,TiN, TaN, WN, TiAlN, TaN, TaC, TaCN, TaSiN, NiSi, CoSi, or a combinationthereof, for example. In some embodiments, the gate electrodes 108, 208,and 308 include metal-containing conductive materials suitable for aPMOS device, such as TiN, WN, TaN, or Ru. In some alternativeembodiments, the first, second, and third gate electrodes 108, 208, and308 include metal-containing conductive materials suitable for an NMOSdevice, such as Ti, Ag, Al, TiAl, TiAlN, TaC, TaCN, TaSiN, Mn, or Zr.The first, second, and third gate electrodes 108, 208, and 308 may beformed by performing a suitable process such as an ALD process, a CVDprocess, a PVD process, a plating process, or a combination thereof.

Referring to FIGS. 3D and 3E, the gate material layer 408, the firstdielectric layer 106 c, the second dielectric layer 206 a, and the thirddielectric layer 306 c are patterned by performing a photolithographicprocess and an etching process, for example, so as to form the firstgate stack 104 in the first region R1, the second gate stack 204 in thesecond region R2, and the third gate stack in the third region R3.

The first, second, and third LDD regions 112, 212, and 312 are formed inthe doped region 101 beside the first gate stack 104, the second gatestack 204, and the third gate stack 304 respectively. The first, second,and third LDD regions 112, 212, and 312 may be formed by performing anion implantation process respectively. In some embodiments, the first,second, and third devices D1, D2, and D3 are PMOS devices, the first,second, and third LDD regions 112, 212, and 312 have p-type dopants,such as boron, BF₂ ⁺, and/or a combination thereof. In some alternativeembodiments, the first, second, and third devices D1, D2, and D3 areNMOS devices, the first, second, and third LDD regions 112, 212, and 312have n-type dopants, such as phosphorus, arsenic, and/or a combinationthereof.

Referring to FIG. 3E, spacers 114, 214, and 314 are formed on the firstgate stack 104, the second gate stack 204, and the third gate stack 304respectively. The spacers 114, 214, and 314 may be formed by forming aspacer material layer on the substrate 100, and then the spacer materiallayer is etched by an anisotropic etch process.

Thereafter, the first, second, and third doped regions 110, 210, and 310are formed in the substrate 100 beside the spacers 114, 214 and 314respectively. The first, second, and third doped regions 110, 210, and310 may be source and drain regions respectively. The first dopedregions 110 and the first LDD regions 112 have the same conductivitytype. Similarly, the second doped regions 210 and the second LDD regions212 have the same conductivity type. The third doped regions 310 and thethird LDD regions 312 have the same conductivity type. The first,second, and third doped regions 110, 210, and 310 may be formed byperforming an ion implantation process respectively. As a result, thefirst device D1, the second device D2, and the third device D3 areformed.

Via the selective implantation of fluorine into the substrate in thefirst region, the first gate dielectric layer in the first region isthicker than the third gate dielectric layer in the third region. As aresult, a device having high gain can be obtained.

FIG. 5A through FIG. 5F are schematic cross-sectional views illustratinga manufacturing process of a semiconductor device according to a thirdembodiment of the disclosure. FIG. 6 is a flowchart illustrating amanufacturing method of the semiconductor device according to the thirdembodiment of the disclosure.

The manufacturing process of the semiconductor device according to thethird embodiment of the disclosure is similar to the manufacturingprocess of the semiconductor device according to the second embodimentof the disclosure. The difference is in the forming method of the firstdielectric layer, the second dielectric layer, and the third dielectriclayer formed in the first region R1, the second region R2, and the thirdregion R3 respectively.

Referring to FIG. 5A and FIG. 6, in step S50, a substrate 100 isprovided. The substrate 100 may include a doped region 101 and isolationstructures (not shown) formed therein. The substrate 100 may include afirst region R1, a second region R2, and a third region R3. In somealternative embodiments, the first region R1 and the third region R3 maybe periphery regions, for example, I/O regions, and the second region R2may be a core region. For example, a first device D1, a second deviceD2, and a third device D3 (shown in FIG. 5F) are to be formed in thefirst region R1, the second region R2, and the third region R3respectively. The first device D1, the second device D2, and the thirddevice D3 may be a first MOS device, a second MOS device, and a thirdMOS device respectively. Further, a threshold voltage of the first MOSdevice in the first region R1 is greater than a threshold voltage of thethird MOS device in the third region R3.

Referring to FIG. 5A and FIG. 6, in step S51, a first mask layer 160having a first opening 162 is formed on the substrate 100. The firstmask layer 160 covers the second region R2 and the third region R3, andthe first opening 162 of the first mask layer 160 exposes the firstregion R1. In some embodiments, the first mask layer 160 is a patternedphotoresist layer.

Referring to FIG. 5A and FIG. 6, in step S52, a first implantationprocess 60 is performed on a surface of the substrate 100 by using thefirst mask layer 160 as a mask. The first implantation process 60 may bean ion implantation process, so that an implantation species isimplanted into the doped region 101 in the first region R1. As a result,a growth promoting region 164 is formed in the doped region 101 in thefirst region R1. The implantation species of the first implantationprocess 60 may include growth promoting species, such as fluorine (F).The first implantation process 60 may be performed at a range of energyvalues and dosages. In some embodiments, the energy values may rangefrom 5 keV to 15 keV, and the dosage may range from 1×10¹⁴/cm² to1×10¹⁶/cm².

Referring to FIG. 5A and FIG. 5B and FIG. 6, in step S53, the first masklayer 160 is removed to expose surfaces of the doped region 101 in thefirst region R1, the second region R2, and the third region R3. Thefirst mask layer 160 may be removed by an ashing process, a wet cleanprocess, or a combination thereof.

Referring to FIG. 5B and FIG. 6, in step S54, a second mask layer 150having a second opening 152 is formed on the substrate 100. The secondmask layer 150 covers the first region R1 and the second region R2, andthe second opening 152 of the mask layer 150 exposes the third regionR3. In some embodiments, the second mask layer 150 is a patternedphotoresist layer.

Referring to FIG. 5B and FIG. 6, in step S55, a second implantationprocess 50 is performed on a surface of the substrate 100 by using thesecond mask layer 150 as a mask. The second implantation process 50 maybe an ion implantation process, so that an implantation species isimplanted into the doped region 101 in the third region R3. In someembodiments, the second implantation process 50 and the firstimplantation process 60 use different implantation species. In the firstimplantation process 60, the growth promoting region 164 is formed. Inthe second implantation process 50, a growth slowing region 154 isformed in the doped region 101 in the third region R3. The implantationspecies of the second implantation process 50 may include a growthslowing species, such as an n-type dopant. The n-type dopant includesphosphorus or arsenic. The second implantation process 50 may beperformed at a range of energy values and dosages. In some embodiments,the energy values may range from 5 keV to 15 keV, and the dosage mayrange from 1×10¹⁴/cm² to 1×10¹⁶/cm².

Referring to FIG. 5C and FIG. 6, in step S56, the second mask layer 150is removed by an ashing process, a wet clean process, or a combinationthereof, for example.

In the above embodiments, the growth promoting region 164 in the firstregion R1 is formed first, and then the growth slowing region 154 in thethird region R3 is formed. However, the disclosure is not limitedthereto. In another embodiment, the growth slowing region 154 in thethird region R3 may be formed first, and then the growth promotingregion 164 in the first region R1 is formed.

Referring to FIG. 5C and FIG. 5D, in step S57, a gate dielectric layerforming process is performed on form a first dielectric layer 106 f, asecond dielectric layer 206 d, and a third dielectric layer 306 f on thedoped region 101 in the first region R1, the second region R2, and thethird region R3 respectively. In some embodiments, the gate dielectriclayer forming process may include the following processes.

Referring to FIG. 5C and FIG. 6, in step S58, a first oxidation processis performed, so as to form a first dielectric layer 106 d, a seconddielectric layer 206 d, and a third dielectric layer 306 d on the dopedregion 101 in the first region R1, the second region R2, and the thirdregion R3. Because the growth slowing region 154 is formed in the thirdregion R3, the third dielectric layer 306 d is thinner than the seconddielectric layer 206 d. Further, because the growth promoting region 164is formed in the first region R1, the first dielectric layer 106 d isthicker than the second dielectric layer 206 d. In some embodiments, thefirst oxidation process is a thermal oxidation process, a hightemperature oxidation process, or a combination thereof. The firstoxidation process may be performed at a temperature range from 800° C.to 1200° C.

Referring to FIG. 5C, FIG. 5D, and FIG. 6, in step S59, a block layer166 having an opening 168 is formed on the substrate 100. The blocklayer 166 covers the second region R2, and the opening 168 of the blocklayer 136 exposes the first region R1 and the third region R3. The blocklayer 166 may be a single layer or multiple layers. In some embodiments,the block layer 166 is formed by a dielectric material layer. Thedielectric material layer may be silicon nitride formed by performing asuitable process such as an ALD process, a CVD process, a PVD process, aplating process, or a combination thereof, for example. Thereafter, thedielectric material layer is patterned by performing a photolithographicprocess and an etching process.

Referring to FIG. 5D and FIG. 6, in step S60, a second oxidation processis performed by using the block layer 166 as a mask, so as to form afirst dielectric layer 106 e and a third dielectric layer 306 e on thedoped region 101 in the first region R1 and the third region R3respectively. The second region R2 is covered by the block layer 166,therefore the thickness of the second dielectric layer 206 d is notincreased significantly. In some embodiments, the second oxidationprocess is a thermal oxidation process, a high temperature oxidationprocess, or a combination thereof. The first oxidation process may beperformed at a temperature range from 800° C. to 1200° C.

As a result, the first dielectric layer 106 f, the second dielectriclayer 206 d, and the third dielectric layer 306 f are formed on thedoped region 101 in the first region R1, the second region R2, and thethird region R3 respectively. The first dielectric layer 106 f includesthe first dielectric layer (first part) 106 d and the first dielectriclayer (second part) 106 e, and the third dielectric layer 306 f includesthe third dielectric layer (first part) 306 d and the third dielectriclayer (second part) 306 e. The first dielectric layer 106 f is thickerthan the third dielectric layer 306 f, and the third dielectric layer306 f is thicker than the second dielectric layer 206 d. In someembodiments, the thickness of the first dielectric layer 106 f is about55 angstroms to about 60 angstroms, the thickness of the thirddielectric layer 306 f is about 41 angstroms to about 51 angstroms, andthe thickness of the second dielectric layer 206 d is about 15 angstromsto about 25 angstroms.

Referring to FIG. 5E, FIG. 5F, and FIG. 6, in step S61 and step S62, theblock layer 136 is removed by an etch process such as an isotropic etchprocess. A first device D1, a second device D2, and a third device D3are formed on the substrate 100 in the first region R1, the secondregion R2, and the third region R3 respectively. The first device D1,the second device D2, and the third device D3 include a first gatedielectric layer 106, a second gate dielectric layer 206, and a thirdgate dielectric layer 306. The first, second, and third gate dielectriclayers 106, 206, and 306 are formed from the first dielectric layer 106f, the second dielectric layer 206 d, and the third dielectric layer 306f. In some embodiments, the first device D1, the second device D2, andthe third device D3 are a first MOS device, a second MOS device, and athird MOS device respectively. The method of forming the first MOSdevice, the second MOS device, and the third MOS device of the thirdembodiment are similar to the first MOS device, the second MOS device,and the third MOS device of the second embodiment.

Via the selective implantation of fluorine into the substrate in thefirst region and the selective implantation of the n-type dopant intothe third region, the difference in the thicknesses of the first gatedielectric layer and the third gate dielectric layer can be moresignificant. As a result, a device having high gain can be obtained.

FIG. 7A and FIG. 7C are schematic cross-sectional views illustratingsemiconductor devices according to a fourth embodiment of thedisclosure. FIG. 7B is a schematic top view illustrating thesemiconductor device of FIG. 7A. FIG. 7D is a schematic top viewillustrating the semiconductor device of FIG. 7C.

Referring to FIG. 7A and FIG. 7C, a substrate 800 is provided. Thematerial of substrate 800 may be similar to that of the substrate 100.The substrate 800 may include various doped regions depending on designrequirements (e.g., p-type substrate or n-type substrate). In someembodiments, a doped region 801, formed in the substrate 800, may be awell, a buried doped region, or a combination thereof. In someembodiments, the doped region 801 and the substrate 800 have the sameconductivity type. In some alternative embodiments, the doped region 801and the substrate 800 have different conductivity types. In someembodiments, the doped region 801 may be doped with p-type or n-typedopants. For example, the doped region 801 may be doped with p-typedopants, such as boron, BF₂ ⁺, and/or a combination thereof; and n-typedopants, such as phosphorus, arsenic, and/or a combination thereof.

Referring to FIG. 7A and FIG. 7C, a semiconductor device D7 is formed onthe substrate 800. The semiconductor device D7 may be a MOS device. Thesemiconductor device D7 may include a gate stack 804 and a plurality ofdoped regions 809. The gate stack 804 includes a gate dielectric layer806 and a gate electrode 808 on the gate dielectric layer 806. In someembodiments, the gate stack 804 of the fourth embodiment may be similarto the first gate stack 104, the second gate stack 204, or the thirdgate stack 304 of the first embodiment. That is, the gate dielectriclayer 806 is similar to the first gate dielectric layer 106, the secondgate dielectric layer 206, or the third gate dielectric layer 306.Similarly, the gate electrode 808 is similar to the first gate electrode108, the second dielectric layer 208, or the third gate dielectric layer308.

Referring to FIG. 7A and FIG. 7C, the plurality of doped regions 809have a same conductivity type dopant therein. In some embodiment, thedevice D7 is a PMOS device, the plurality of doped regions 809 havep-type dopants, such as boron, BF₂ ⁺, and/or a combination thereof. Insome alternative embodiments, the device D7 is a NMOS device, and theplurality of doped regions 809 have n-type dopants, such as phosphorus,arsenic, and/or a combination thereof.

Referring to FIG. 7A and FIG. 7C, the plurality of doped regions 809 areformed in the substrate 800. The plurality of doped regions 809 includea first doped region 810 a, a second doped region 810 b, a first lightlydoped region 812 a, and a second lightly doped region 812 b. The firstdoped region 810 a is formed in the substrate 800 at a first side of thegate stack 804. The second doped region 810 b is formed in the substrate800 at a second side of the gate stack 804. In some embodiments, thefirst doped region 810 a and the second doped region 810 b have similarproperties. For example, the properties include at least one of aconcentration, a depth, a profile, a cross-section area or a combinationthereof.

Referring to FIG. 7A and FIG. 7C, the first lightly doped region 812 ais formed in the substrate 800 at the first side of the gate stack 804.The second doped lightly doped region 812 b is formed in the substrate800 at the second side of the gate stack 804. In other words, the firstlightly doped region 812 a is formed in the substrate 800 between thegate stack 804 and the first doped region 810 a. The second lightlydoped region 812 b is formed in the substrate 800 between the gate stack804 and the second doped region 810 b. A property of the first lightlydoped region 812 a is different from a property of the second lightlydoped region 812 b. For example, the property includes at least one of aconcentration, a depth, a profile, a cross-section area or combinationthereof.

Referring to FIG. 7A and FIG. 7C, in some embodiments, the first lightlydoped region 812 a is a lightly doped source region and the secondlightly doped region 812 a is a lightly doped drain region, and aconcentration of the first lightly doped region 812 a is greater than aconcentration of the second lightly doped region 812 b.

Referring to FIG. 7A and FIG. 7C, in some alternative embodiments, thefirst lightly doped region 812 a is a lightly doped source region andthe second lightly doped region 812 a is a lightly doped drain region,and a depth d1 of the first lightly doped region 812 a is greater than adepth d2 of the second lightly doped region 812 b.

Referring to FIG. 7A and FIG. 7C, in yet some other alternativeembodiments, a profile of the first lightly doped region 812 a isdifferent from a profile of the second lightly doped region 812 b.

Referring to FIG. 7A to FIG. 7D, in yet some other alternativeembodiments, the first lightly doped region 812 a is a lightly dopedsource region and the second lightly doped region 812 a is a lightlydoped drain region, and a cross-section area A1 of the first lightlydoped region 812 a is greater than a cross-section area A2 of the secondlightly doped region 812 b.

Referring to FIG. 7A to FIG. 7D, in yet some other alternativeembodiments, the first lightly doped region 812 a is a lightly dopedsource region and the second lightly doped region 812 a is a lightlydoped drain region, and a width W1 of the first lightly doped region 812a is greater than a width W2 of the second lightly doped region 812 b.

Referring to FIG. 7A and FIG. 7B, a first portion P1 of the firstlightly doped region 812 a and a second portion P2 of the second lightlydoped region 812 b may covered by the gate stack 804. In someembodiments, the first lightly doped region 812 a is a lightly dopedsource region and the second lightly doped region 812 a is a lightlydoped drain region, and the first portion P1 is larger than the secondportion P2.

Referring to FIG. 7C and FIG. 7D, in some alternative embodiments, thefirst lightly doped region 812 a is covered by the gate stack 804, butthe second lightly doped region 812 b is not covered by the gate stack804. In other words, the first lightly doped region 812 a has a portionP1 that is covered by the gate stack 804, and the second lightly dopedregion 812 b has no area covered by the gate stack 804.

Referring to FIG. 7A and FIG. 7C, in some embodiments, the semiconductordevice D7 may further include a first pocket region 816 a and a secondpocket region 816 b. The conductivity type of the first pocket region816 a and the second pocket region 816 b are different form theconductivity type of the plurality of doped regions 809. In someembodiments, the plurality of doped regions 809 have first conductivitytype dopants, and the first pocket region 816 a and the second pocketregion 816 b have second conductivity type dopants. The secondconductivity type is opposite to the first conductivity type. In otherwords, the device D7 is a PMOS device, the first pocket region 816 a andthe second pocket region 816 b have n-type dopants, such as phosphorus,arsenic, and/or a combination thereof. In some alternative embodiments,the device D7 is an NMOS device, and the first pocket region 816 a andthe second pocket region 816 b have p-type dopants, such as boron, BF₂⁺, and/or a combination thereof. A property of the first pocket region816 a is different from a property of the second pocket region 816 b.For example, the property includes at least one of a concentration, adepth, a profile, a cross-section area or a combination thereof.

In some embodiments, the first lightly doped region 812 a is a lightlydoped source region and the second lightly doped region 812 a is alightly doped drain region, and a concentration of the first pocketregion 816 a is greater than a concentration of the second pocket region816 b.

In some alternative embodiments, the first lightly doped region 812 a isa lightly doped source region and the second lightly doped region 812 ais a lightly doped drain region, and a depth d3, a width W3, orcross-section area of the first pocket region 816 a is greater than adepth d4, a width W4, or cross-section area of the second pocket region816 b.

In other words, the first lightly doped region 812 a and the secondlightly doped region 812 b are asymmetric, and the first pocket region816 a and the second pocket region 816 b are also asymmetric.

Referring to FIG. 7A to FIG. 7D, in some embodiments, the semiconductordevice D7 may further include spacers 814 formed at sidewalls of thegate stack 804. The spacers 814 may be similar to the first spacers 114,the second spacers 214, or the third spacers 314.

FIG. 8 is a flowchart illustrating a manufacturing method of thesemiconductor devices according to the fourth embodiment of thedisclosure.

Referring to FIG. 7 A, FIG. 7C and FIG. 8, in step S80, the substrate800 is provided. In step S81, the gate stack 804 is formed on thesubstrate 800. The method of forming the gate stack 804 includes thefollowing processes. First, a gate dielectric material layer is formedon the substrate 800 and a gate material layer on the gate dielectricmaterial layer. The gate dielectric material layer and the gate materiallayer are patterned by performing a photolithographic process and anetching process, for example.

Referring to FIG. 7 A, FIG. 7C, and FIG. 8, in step S82, a first lightlydoped region 812 a and a second lightly doped region 812 b are formed bydifferent processes. In addition, a first pocket region 816 a and asecond pocket region 816 b are formed by different processes.

The first lightly doped region 812 a and the first pocket region 816 amay be formed by the following processes. A first mask layer is formedto cover the substrate 800 at the second side of the gate stack 804.Then, a first implantation process such as an ion implantation processis performed on the substrate 800 with the first mask layer as a mask soas to form the first lightly doped region 812 a in the substrate 800 atthe first side of the gate stack 804. Thereafter, a first pocketimplantation process such as an ion implantation process is performed onthe substrate 800 with the first mask layer as a mask so as to form thefirst pocket region 816 a adjacent to the first lightly doped region 812a.

Similarly, the second lightly doped region 812 b and the second pocketregion 816 a may be formed by the following processes. A second masklayer is formed to cover the substrate 800 at the first side of the gatestack 804. Then, a second implantation process such as an ionimplantation process is performed on the substrate 800 with the secondmask layer as a mask, so as to form the second lightly doped region 812b in the substrate 800 at the second side of the gate stack 804.Thereafter, a second pocket implantation process such as an ionimplantation process is performed on the substrate 800 with the secondmask layer as a mask so as to form the second pocket region 816 badjacent to the second lightly doped region 812 b.

The first implantation process and the second implantation process areperformed at different ranges of energy values and/or dosages. In someembodiments, first energy values and/or a first dosage of the firstimplantation process is greater than second energy values and/or asecond dosage of the second implantation process. For example, the firstenergy values may range from 6 keV to 12 keV, and the second energyvalues may range from 4 keV to 8 keV; and the first dosage may rangefrom 5×10¹³/cm² to 5×10¹⁴/cm², and the second dosage may range from5×10¹²/cm² to 5×10¹³/cm². For example, a ratio of the first energyvalues of the first implantation process to the second energy values ofthe second implantation process is about 1.5 to 2.5, and a ratio of thefirst dosage of the first implantation process to the second dosage ofthe second implantation process is about 5 to 15.

Similarly, the first pocket implantation process and the second pocketimplantation process are performed at different ranges of energy valuesand/or dosages. In some embodiments, first energy values and/or a firstdosage of the first pocket implantation process is greater than secondenergy values and/or a second dosage of the second pocket implantationprocess. For example, a ratio of the first energy values of the firstpocket implantation process to the second energy values of the secondpocket implantation process is about 1.5 to 2.5, and a ratio of thefirst dosage of the first pocket implantation process to the seconddosage the second pocket implantation process is about 5 to 15.

Referring to FIG. 7A, FIG. 7C, and FIG. 8, in step S83, the spacers 814are formed at the sidewalls of the gate stack 804. In step S84, a firstdoped region 810 a and a second doped region 810 b are formed. In someembodiments, the first doped region 810 a and the second doped region810 b may be formed by a same third implantation process such as an ionimplantation process, so that the first doped region 810 a and thesecond doped region 810 b are formed at the same time. In someembodiments, third energy values and/or a third dosage of the same thirdimplantation process are/is greater than the first and second energyvalues and/or the first and the second dosages of the first and thesecond implantation processes.

By varying the properties of the LDDs, Gm/Id of the device can beenhanced. As a result, a device having high gain can be obtained.

FIG. 9A to FIG. 9C are schematic cross-sectional views illustrating asemiconductor device according to a fifth embodiment of the disclosure.FIG. 10 is a flowchart illustrating a manufacturing method of thesemiconductor device according to the fifth embodiment of thedisclosure.

Referring to FIG. 9A and FIG. 10, in step S90, a substrate 900 isprovided. The material of substrate 900 may be similar to that of thesubstrate 100. The substrate 900 may include various doped regionsdepending on design requirements (e.g., p-type substrate or n-typesubstrate). In some embodiments, a doped region 901, formed in thesubstrate 900, may be a well. In some embodiments, the doped region 901and the substrate 900 have the same conductivity type. In somealternative embodiments, the doped region 901 and the substrate 900 havedifferent conductivity types. In some embodiments, the doped region 901may be doped with p-type or n-type dopants. For example, the dopedregion 901 may be doped with p-type dopants, such as boron, BF₂ ⁺,and/or a combination thereof; and n-type dopants, such as phosphorus,arsenic, and/or a combination thereof.

Referring to FIG. 9A and FIG. 10, in step S91, a buried doped region 903is formed in the doped region 901. The buried doped region 903 may bedoped with p-type or n-type dopants. In some embodiments, the burieddoped region 903 include p-type dopants for an PMOS device, such asboron, BF₂ ⁺, and/or a combination thereof. In some alternativeembodiments, the buried doped region 903 includes n-type dopants for anNMOS device, such as phosphorus, arsenic, and/or a combination thereof.The buried doped region 903 may be formed by performing a firstimplantation process 910. The first implantation process 910 may be acounter-doping process performed at a range of first energy values andfirst dosages. In some embodiments, the first energy values may rangefrom 10 keV to 50 keV, and the first dosage may range from 1×10¹³/cm² to1×10¹⁵/cm². The buried doped region 903 is separated from the gate stack904 by a distance d9. The distance d9 is about 50 nm to 60 nm, forexample. A thickness t1 of the buried doped region 903 ranges from 5 nmto 10 nm, for example.

Referring to FIG. 9C and FIG. 10, in step S92, a device D9 is formed onthe substrate 900. In some embodiments, the device D9 is a MOS device.The method of forming the MOS device of the fifth embodiment is similarto the first MOS device, the second MOS device, or the third MOS deviceof the second embodiment. The device D9 may be formed by the followingprocess.

Referring to FIG. 9B and FIG. 10, in step S93, a gate stack 904 isformed on the substrate 900. The gate stack 904 includes a gatedielectric layer 906 and a gate electrode 908. In some embodiments, thegate electrode 908 may be doped with p-type or n-type dopants. In someembodiments, the gate electrode 908 includes p-type dopants for an NMOSdevice, such as boron, BF₂ ⁺, and/or a combination thereof. In somealternative embodiments, the gate electrode 908 includes n-type dopantsfor a PMOS device, such as phosphorus, arsenic, and/or a combinationthereof.

The method of forming the gate stack 904 includes the following process.First, a gate dielectric material layer is formed on the doped region901 and a gate material layer on the gate dielectric material layer. Thegate dielectric material layer and the gate material layer are patternedby performing a photolithographic process and an etching process so asto form the gate dielectric layer 906 and the gate electrode 908.

Referring to FIG. 9B and FIG. 10, in step S94, a first lightly dopedregion 912 a and a second lightly doped region 912 b are formed in thedoped region 901 at a first side and a second side of the gate stack 904respectively. The first lightly doped region 912 a and the secondlightly doped region 912 b may be doped with p-type or n-type dopants.In some embodiments, the first lightly doped region 912 a and the secondlightly doped region 912 b include p-type dopants for a PMOS device,such as boron, BF₂ ⁺, and/or a combination thereof. In some alternativeembodiments, the first lightly doped region 912 a and the second lightlydoped region 912 b include n-type dopants for an NMOS device, such asphosphorus, arsenic, and/or a combination thereof. The first lightlydoped region 912 a and the second lightly doped region 912 b may beformed by performing a second implantation process 920 such as an ionimplantation. In some embodiment, second energy values of the secondimplantation process 920 may range from 5 keV to 10 keV, and seconddosage of the second implantation process 920 may range from 5×10¹²/cm²to 5×10¹³/cm². The first lightly doped region 912 a and the secondlightly doped region 912 b are formed above the buried doped region 903.

Referring to FIG. 9C and FIG. 10, in step S95, the spacers 914 areformed at the sidewalls of the gate stack 904 in the doped region 901beside the spacers 914. In step S96, the first doped region 910 a andthe second doped region 910 b are formed. In some embodiments, the firstdoped region 910 a and the second doped region 910 b include p-typedopants for a PMOS device, such as boron, BF₂ ⁺, and/or a combinationthereof. In some alternative embodiments, the first doped region 910 aand the second doped region 910 b include n-type dopants for an NMOSdevice, such as phosphorus, arsenic, and/or a combination thereof. Insome embodiments, the first doped region 910 a and the second dopedregion 910 b may be formed by a third implantation process 930 such asan ion implantation process, so that the first doped region 910 a andthe second doped region 910 b are formed. In some embodiments, thirdenergy values and/or a third dosage of the third implantation process930 are/is greater than the second energy values and/or the seconddosages of the second implantation process 920. The third energy valuesof the third implantation process 930 is greater than or the same as thefirst energy values of the first implantation process 910. The thirddosage of the third implantation process 930 is less than the firstdosage of the first implantation process 910.

The buried doped region 903 is located in the doped region 901 under thegate stack 904, the first lightly doped region 912 a and the secondlightly doped region 912 b.

The buried doped region 903, the first lightly doped region 912 a, thesecond lightly doped region 912 b, the first doped region 910 a, and thesecond doped region 910 b have the same conductivity dopants. In someembodiments, the buried doped region 903, the first lightly doped region912 a, the second lightly doped region 912 b, the first doped region 910a, and the second doped region 910 b are of a first conductivity type,the doped region 901 or the substrate 900 is of a second conductivitytype, and the gate electrode 908 is of the second conductivity type. Thesecond conductivity type is opposite to the first conductivity type.

The doping concentration of the buried doped region 903 is less than thedoping concentration of the first doped region 910 a and the seconddoped region 910 b. Further, the buried doped region 903 extends fromthe first doped region 910 a to the second doped region 910 b. In someembodiments, the buried doped region 903 is in physical contact with thefirst doped region 910 a and the second doped region 910 b to serve as aburied channel under a surface channel which is between the first dopedregion 910 a and the second doped region 910 b and under the gate stack904.

Because the buried channel is away from an interface between thesubstrate and the gate dielectric layer, current can be away from thegate dielectric layer, and therefore damage to the gate dielectric layer906 may be reduced. As a result, device noise can be reduced.

The present disclosure is not limited to applications in which thesemiconductor device includes MOSFETs, and may be extended to FinFETs.

In accordance with some embodiments of the present disclosure, asemiconductor device includes a gate stack, a first doped region, asecond doped region, a first lightly doped region and a second lightlydoped region. The gate stack is disposed on a substrate. The first dopedregion is located in the substrate at a first side of the gate stack.The second doped region is located in the substrate at a second side ofthe gate stack. The first lightly doped region is located in thesubstrate between the gate stack and the first doped region. The secondlightly doped region is located in the substrate between the gate stackand the second doped region. A property of the first lightly dopedregion is different from a property of the second lightly doped region.

In accordance with alternative embodiments of the present disclosure, asemiconductor device includes a substrate, a gate stack, a lightly dopedsource region, and a lightly doped drain region. The gate stack isdisposed on the substrate. The lightly doped source region is located inthe substrate and at a first side of the gate stack. The lightly dopeddrain region is located in the substrate at a second side of the gatestack. The lightly doped source region and the lightly doped drainregion are asymmetric.

In accordance with some embodiments of the disclosure, a method offorming a semiconductor device is provided as below. A substrate isprovided. A gate stack is formed on the substrate. A first implantationprocess is performed to form a lightly doped source region in thesubstrate at a first side of the gate stack. A second implantationprocess is performed to form a lightly doped drain region in thesubstrate at a second side of the gate stack. A first process parameterof the first implantation process is different from a second processparameter of the second implantation process.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device, comprising: a gate stack,disposed on a substrate; a first doped region, located in the substrateat a first side of the gate stack; a second doped region, located in thesubstrate at a second side of the gate stack; a first lightly dopedregion, located in the substrate between the gate stack and the firstdoped region; and a second lightly doped region, located in thesubstrate between the gate stack and the second doped region, wherein aproperty of the first lightly doped region is different from a propertyof the second lightly doped region.
 2. The semiconductor deviceaccording to claim 1, wherein the property comprises at least one of aconcentration, a depth, a profile, a cross-section area or a combinationthereof.
 3. The semiconductor device according to claim 1, wherein afirst portion of the first lightly doped region and a second portion ofthe second lightly doped region are covered by the gate stack, and thefirst portion is larger than the second portion.
 4. The semiconductordevice according to claim 1, wherein a portion of the first lightlydoped region is covered by the gate stack, and the second lightly dopedregion is not covered by the gate stack.
 5. The semiconductor deviceaccording to claim 1, further comprising: a first pocket region, locatedin the substrate adjacent to the first lightly doped region; and asecond pocket region, located in the substrate adjacent to the secondlightly doped region, wherein a property of the first pocket region isdifferent from a property of the second pocket region.
 6. Asemiconductor device, comprising: a substrate; a gate stack, disposed onthe substrate; a lightly doped source region, located in the substrateand at a first side of the gate stack; and a lightly doped drain region,located in the substrate at a second side of the gate stack, wherein thelightly doped source region and the lightly doped drain region areasymmetric.
 7. The semiconductor device of claim 6, wherein aconcentration of the lightly doped source region is larger than aconcentration of the lightly doped drain region.
 8. The semiconductordevice of claim 6, wherein a depth of the lightly doped source region islarger than a depth of the lightly doped drain region.
 9. Thesemiconductor device of claim 6, wherein a width of the lightly dopedsource region is larger than a width of the lightly doped drain region.10. The semiconductor device of claim 6, wherein a profile of thelightly doped source region is different from a depth of the lightlydoped drain region.
 11. The semiconductor device of claim 6, wherein across-section area of the lightly doped source region is larger than across-section area of the lightly doped drain region.
 12. Thesemiconductor device of claim 6, wherein a first portion of the lightlydoped source region and a second portion of the lightly doped drainregion are covered by the gate stack, and an area of the first portionis larger than an area of the second portion.
 13. The semiconductordevice of claim 6, wherein a portion of the lightly doped source regionis overlapped with the gate stack, and the lightly doped drain region isnot overlapped with the gate stack.
 14. A semiconductor device of claim6, further comprising: a first pocket region, located in the substrateadjacent to the lightly doped source region; and a second pocket region,located in the substrate adjacent to the lightly doped drain region,wherein a property of the first pocket region is different from aproperty of the second pocket region.
 15. A method of forming asemiconductor device, comprising: providing a substrate; forming a gatestack on the substrate; performing a first implantation process to forma lightly doped source region in the substrate at a first side of thegate stack; and performing a second implantation process to form alightly doped drain region in the substrate at a second side of the gatestack; wherein a first process parameter of the first implantationprocess is different from a second process parameter of the secondimplantation process.
 16. The method of claim 15, further comprising:forming a first mask layer to cover the substrate at the second side ofthe gate stack before performing the first implantation process;performing the first implantation process with the first mask layer as amask; and removing the first mask layer.
 17. The method of claim 16,further comprising: forming a second mask layer to cover the substrateat the first side of the gate stack before performing the secondimplantation process; performing the second implantation process withthe second mask layer as a mask; and removing the second mask layer. 18.The method of claim 15, wherein a first energy value and a first dosageof the first implantation process are different from a second energyvalue and a second dosage of the second implantation process.
 19. Themethod of claim 18, wherein the first energy value of the firstimplantation process is larger than the second energy value of thesecond implantation process.
 20. The method of claim 18, wherein thefirst dosage of the first implantation process is larger than the seconddosage of the second implantation process.